For the preparation of, e.g., printed circuits, an image-forming method has been developed comprising adhering an image-forming material, comprising a transparent support having adhered thereon a photopolymerizable composition layer, onto the surface of an image-forming substrate in such a manner that the photopolymerizable composition layer is in contact with the substrate; imagewise exposing the photopolymerizable composition layer to form the corresponding cured areas and; if necessary, heating the image-forming material; and peeling away the support from the substrate to form a resist image on the substrate.
In image-forming materials of the type as described above, the cohesive strength of the photopolymerizable composition layer is generally set at a relatively low level so that the unexposed areas of the photopolymerizable composition layer can be easily separated from the exposed areas, i.e., cured areas, even if the support is peeled away from the substrate at any peel angle. However, this causes the problem that at any portions of the unexposed areas of the photopolymerizable composition layer, a sharp image line cannot be formed. Hence, from the viewpoint of forming sharp images, it is desirable for the above-described cohesive strength to be increased so that the unexposed areas can be sharply separated from the exposed areas.
When the cohesive strength of the photopolymerizable composition layer is set at a high level, sharp image lines can be formed since the stress caused in the photopolymerizable composition layer during the peeling operation can be concentrated at the boundaries between the exposed areas and the unexposed areas, although some difficulty is encountered in the separation of the unexposed areas from the exposed areas. If the cohesive strength is increased excessively, the separation of the unexposed areas from the exposed areas becomes more difficult. For example, in pattern 1 with many corners as shown in FIG. 1, residual strips 2 of the unexposed areas tend to remain at the sides of edges in the peeling direction (indicated by an arrow (a)) of the corners.
Extensive investigations have been conducted on the problem of making the unexposed areas of the photopolymerizable composition layer easily separable from the exposed areas and forming sharp images by increasing the cohesive strength to achieve the present invention.